Musk, who is chief executive of electric car company Tesla, rocket manufacturer SpaceX and a tunnel boring company, revealed his ambitious two-year timeline during a Ted talk. Musk has previously said that the hardware fitted to all new Teslas sold today will be sufficient to enable Level Five autonomous driving in the years to come, once software and road legislation has caught up.

But even before mid-2019, Musk believes Tesla will have created a test vehicle capable of driving itself "from a parking lot in California to a parking lot in New York [with] no controls touched at any point during the entire journey." In this scenario, which is below Level Five, the driver would have to remain alert and ready to take over in extreme environments only.

Elon Musk

Musk went on: "The real trick of it is how you make it work [more than] 99.9% of the time, because say if a car crashes one in a thousand times then you're probably still not going to be comfortable falling asleep. And you shouldn't be, certainly. It's never going to be perfect, no system is going to be perfect."

But there is a level of risk which Musk believes customers travelling in autonomous cars will be willing to accept. "But if you say the car is unlikely to crash in 100 lifetimes or 1,000 lifetimes, people will think 'ok, wow. If I live for 1,000 lifetimes and I'm still unlikely to experience a crash, that's probably ok'".